Brill et al.: Effects of rapid decompression and exposure to bright light on visual function in Sebastes melanops and Hippoglossus stenolepis 435 
conduct the requisite experiments. Pacific halibut are 
less able to detect baits in near total darkness than 
at brighter light levels (Stoner, 2003). By extension, 
we conclude that individuals whose visual function 
has been compromised by exposure to bright light will 
be less able to feed and avoid predators than normal 
animals. Behavioral tests quantifying the effects of 
bright light exposure on the ability of Pacific halibut to 
locate and capture prey or detect predators are clearly 
warranted. 
To the best of our knowledge, there are no published 
descriptions of retinal anatomy in Pacific halibut. The 
retinas of Atlantic halibut (Hippoglossus hippoglossus ) 
contain both rods and cones (Kvenseth et al., 1996), 
and we strongly suspect that the retinas of Pacific 
halibut do also. Likewise, we know of no microspectro- 
photometry studies detailing the absorbance maxima 
of photopigments in juvenile or adult Pacific halibut 
retinas. Microspectrophotometry studies of other mem- 
bers of the family Pleuronectidae ( Platichthys flesus 
[flounder] and Pseudopleuronectes americanus [win- 
ter flounder]) show that the peak absorbance of the 
photopigment in rod cells is =510 nm, that in single 
cones is =450 nm, and that in double cones is =530 
or 550 nm (Evans et al., 1993; Jokela-Maatta et al., 
2007). From these lines of evidence, and the results 
obtained by fitting rhodopsin absorbance templates to 
the ERG data by the maximum likelihood method (Fig. 
4), we concluded that Pacific halibut retinas contain 
two photopigments with absorbance maxima similar 
to other members of the family Pleuronectidae. Our 
conclusion is also in general agreement with the maxi- 
mum spectral sensitivities of a range of coastal and 
continental shelf species (Levine and MacNichol, 1979; 
Bowmaker, 1990). 
The change in spectral sensitivity curves of Pacific 
halibut (Fig. 3) caused by exposure to bright light and 
the results of photopigment template fitting (Fig. 4) 
imply that it is the functional properties of a single 
class of cells (those containing the longer wavelength 
=520 to 540 nm photopigment) which are predominate- 
ly disrupted by exposure to bright light. The retinas 
of larval Atlantic halibut and adults of the related 
species — winter flounder — are dominated by the so- 
called “green cones” (Evans et ah, 1993; Helvik et al., 
2001). If this is also the case in Pacific halibut, our 
results indicate disruption of the photoreceptor cells 
which normally provide maximal quantal absorption 
in the green-light dominated coastal waters (Levine 
and MacNichol, 1979; Lythgoe, 1975, 1980; Crescitelli, 
1991). This detriment to vision is likely to have severe 
consequences for postrelease predator avoidance and 
foraging success. Moreover, the results from phot- 
opigment template fitting indicate that the specific 
functional deficit persists for at least 10 to 12 hours 
after the exposure to bright light and worsens with 
time (Fig. 4). If this diminished functionality is due to 
apoptosis induced by photic injury (Wu et ah, 2006), it 
is likely that it will continue to worsen progressively 
and be permanent. 
Hook-and-line caught Pacific halibut can be discarded 
quickly and are not subject to significant time periods 
out of the water (Kaimmer and Trumble, 1998). Be- 
cause they would not be exposed to direct sunlight for 
prolonged periods, minimal or no reduction in visual 
function would be expected. In contrast, trawl-caught 
Pacific halibut can be exposed to bright light during 
prolonged sorting operations (Davis and Olla, 2001). 
Increased mortality has been demonstrated in Pacific 
halibut that remain on deck for 20-40 min (Trumble 
et al., 1995). Although the exact causes are unknown, 
our results clearly imply that these fish could have 
had significant visual impairment when discarded. De- 
velopment of procedures to improve survival of Pacific 
halibut may therefore require not only reducing sort- 
ing time (and therefore reducing exposure to air and 
extreme temperatures), but also sheltering the fish from 
bright light. 
The low flicker fusion frequency and high light sen- 
sitivity of Pacific halibut are characteristics of a visual 
system adapted to function at low light levels (War- 
rant, 1999). We hypothesize that these features make 
Pacific halibut, and other demersal fishes with similarly 
structured visual systems, more susceptible to damage 
by exposure to direct sunlight than species normally 
inhabiting brightly lit environments. Should this be the 
case, there would be significant implications for fishery 
management, although obviously many significant ques- 
tions remain. For example, we do not know how long in- 
dividuals have to be exposed to direct sunlight to incur 
deficits in visual acuity, nor do we know the threshold 
of light intensity that causes retinal damage. Research 
is also warranted on exactly which of the various cell 
types within the retina are being damaged, the effect(s) 
of light-induced visual deficits on predator-avoidance 
and prey-finding behaviors, the resultant changes in 
rates of mortality, and possible effects at the popula- 
tion level. 
Acknowledgments 
This project was funded by Alaska Fisheries Science 
Center, National Marine Fisheries Service, National 
Oceanic and Atmospheric Administration. All proce- 
dures described herein were approved by the Oregon 
State University Institutional Animal Care and Use 
Committee (ACUP 3577), and comply with all appli- 
cable U.S. laws and regulations. The views expressed 
herein are those of the authors and do not necessarily 
reflect the views of NOAA or any of its sub-agencies. 
The authors gratefully acknowledge the hospitality 
of the staff of the Hatfield Marine Science Center 
(Newport, Oregon), and A. Horodysky for his efforts to 
initiate this project, his comments on earlier drafts of 
this manuscript, and his help with the photopigment 
template fitting procedures. R. Latour developed the 
R-code required for photopigment template fitting. 
This is contribution 2938 from the Virginia Institute 
of Marine Science. 
